The present invention relates to a variable venturi-type carburetor.
In a variable venturi-type carburetor, in the case wherein the suction piston is so formed that the tip face thereof, which is located upstream of the needle fixed onto the needle-mounting face of the suction piston, projects from the needle-mounting face towards the tip of the needle so as to define the venturi portion between the projecting portion of the tip face of the suction piston and the inner wall of the intake passage, since the upstream side of the needle is covered by the projecting portion of the tip face of the suction piston when the amount of air fed into the cylinder of an engine is small, a problem occurs in that it is difficult to sufficiently vaporize fuel injected from the nozzle. In addition, in the case wherein the variable venturi-type carburetor is a carburetor of the downdraft type, part of the fuel fed from the nozzle flows on the needle and adheres to the needle-mounting face of the suction piston. The fuel adhering to the needle-mounting face then falls off in the form of droplets, and the air-fuel ratio of the mixture fed into the cylinder of the engine fluctuates particularly when the amount of air fed into the cylinder of the engine is small and, as a result, a problem occurs in that the exhaust emission deteriorates.